Delay Exhaustion

A target you can see within range stops feeling any ill effects from fatigue or exhaustion.

The target will continue to make saving throws to avoid exhaustion and any effects caused by extreme exertion, but the effects will not occur until this spell ends, at which point any damage or results of exhaustion will all occur at once.

A creature could therefore fail six saving throws to avoid exhaustion over the course of an 8-hour swim, complete the swim, and then suddenly die of exhaustion when this spell ends.

Credit- Dungeon Masters Guild: Underwater Campaign; Daniel Chivers